Fuel injection control systems and methods for internal combustion engines are well-known in the art, for instance from EP-1 336 745 B1.
In conventional internal combustion engines, the quantity of fuel actually injected into each cylinder and at each injection may be different from the nominal fuel quantity requested by the electronic control unit (ECU) and which is used to determine the energization time of the injectors.
There are several factors which contribute to this difference, particularly the dispersion of the injectors' characteristics, due to the production process spread, and the time-drift variations of the same characteristics, due to aging of the injection system. In fact, the current injector production processes are not accurate enough to produce injectors with tight tolerances; moreover, these tolerances become worse with aging during the injector life-time. As a result, for a given energization time and a given rail pressure, the quantity of fuel actually injected may be different from one injector to another.
The control unit contains exhaust emission relevant maps in which different engine parameters (i.e., set points) are related to the nominal injected fuel quantity and the nominal engine speed. Examples of such set points are the amount of exhaust gas recirculation, the boost pressure, the rail pressure, the throttle valve position. When a difference between the actually injected fuel quantity and the nominal fuel quantity occurs, an incorrect value of this quantity is used to read the emission maps (i.e., that is an incorrect value of said set points is associated to the actually injected fuel quantity), and this results in emission worsening.
In view of the above, it is at least one object of the present invention to provide an improved method for operating an internal combustion engine to recover the injectors' drifts. In addition, other objects, desirable features, and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.